In a small mobile terminal such as mobile phone, a PHS (Personal Handy Phone System), and a PDA (Personal Digital Assistant), tendency of a small size and a thin structure is accelerating. For the purpose of realization of a small mobile terminal with the small size and thin structure, the small size and thin structure of a functional part, the thin structure of a printed circuit board on which the functional parts are mounted, the small size of an antenna, and the thin structure of a housing which accommodates the functional parts and the printed circuit board and so on are carried forward.
FIG. 1 is a cross sectional view of a conventional small mobile terminal. As shown in FIG. 1, in the conventional small mobile terminal, generally, a front housing 501, switch buttons 525, a key sheet 502, switch domes 524, a switch board 555, a printed circuit board 504 on which electronic parts 503 are mounted are stacked in the direction of the thickness to be fixed on a back housing 558. Many through-holes exist in the front housing 501 and the switch buttons 525 are provided for the through-holes. Wiring line patterns 522A and 522B are formed on the surface of the switch board 555. The switch dome 524 is formed of an elastically deformable conductive material and the periphery of the switch dome 524 is connected with the wiring line pattern 522A. When the switch button 525 is pushed, the switch dome 524 transforms elastically through the key sheet 502, and the center portion of the switch dome 524 contacts the wiring line pattern 522B so that the wiring line patterns 522A and 522B are set to an electrically conductive state. In this way, predetermined data can be inputted. With the housing, the structure is demanded in which the thickness of the whole mobile equipment is made thin while maintaining mechanical strength. Conventionally, for the purpose of maintenance of the housing stiffness, reinforcement ribs are increased and reinforcement is carried out using components, as described in Japanese Laid Open Patent Application (JP-P2000-151136A).
In the conventional small mobile terminal shown in FIG. 1, many through-holes exist in the housing as described above. This causes large degradation of the stiffness of the front housing 501. Also, as shown in FIG. 1, generally, the switch button 525 has the thickness of about 1.4 mm, the key sheet 502 has the thickness of about 0.7 mm, the switch dome 524 has the height of about 0.3 mm, and the switch board 555 has the thickness of about 0.8 mm. The total thickness t2 of them is about 3.2 mm. These components tend to be made thin for the thin structure of the small mobile terminal. However, the thin structure degrades flexural rigidity and twisting stiffness of those components and these components have a possibility to be transformed or damaged. Especially, the housing is easy to transform through a switch operation by a user or by external force, because it has many through-holes for the switch buttons 525, in spite that the housing has an important function to prevent its own transformation and the transformation of the board 504. Thus, the transformation of the housing results in the transformation of the components mechanically connected with the housing. Especially, when the board 504 is transformed, peeling of solders from the electronic part 503 and the wiring line occurs because many electronic parts 503 are mounted on the board 504 and the wiring lines are provided. As a result, there is a possibility of occurrence of a trouble in the mobile terminal. Also, to use a rib and so on to prevent the occurrence of such a situation is a factor that hinders the thin structure of the equipment.
In conjunction with the above description, an operation unit of a mobile phone is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 7-58815). In this conventional example, a main board is accommodated in a cabinet body. An operation section concave section is formed on the cabinet body. On an operation section printed circuit board, a plurality of operation contacts are printed and LEDs are mounted. An operation button sheet is formed of a material having a light transmitting property and elasticity, and has a key top, on which light shielding print is carried out to leave predetermined numbers or characters, in positions corresponding to the operation contacts. An operation button cover has an opening in a location corresponding to the key top and has a pushing rib to push the operation button sheet on a lower surface of the button cover in the opening.
Also, a portable phone is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 10-276249). The portable phone of this conventional example is composed of an upper stage printed circuit board and a lower stage printed circuit board in a flat casing. A shield chassis is interposed between the printed circuit boards. A switch sheet has a plurality of switches for key input of a telephone number and is supported by a shield and sheet support board. A cell box has an upwardly projecting portion on the side of the upper stage printed circuit board and is provided below the lower stage printed circuit board. The shield chassis and the lower stage printed circuit board have blanked portions corresponding to the upwardly projecting portion of the cell box. The cell box is provided in a part non-existing region on the back side of the upper stage printed circuit board through the blanked portions of the shield chassis and the lower stage printed circuit board.
Also, a data input key is disclosed in Japanese Laid Open Patent Application (JP-A-Heisei 11-149841). The data input key of this conventional example has a key top formed of a light transmissible resin, and a light transmissible resin sheet on which a print is carried out and the key top is provided on the light transmissible resin sheet.
Also, a mobile terminal apparatus is disclosed in Japanese Laid Open Patent Application (JP-P2000-151136A). The mobile terminal apparatus of this conventional example has a printed circuit board on which parts are mounted, a lower case which has ribs to receive the parts in correspondence to the arrangement positions of the parts, and a battery case provided below the lower case to prevent the transformation of the lower case.
Also, a housing structure of a mobile terminal is disclosed in Japanese Laid Open Patent Application (JP-P2001-119455A). In this conventional example, the housing structure of the mobile terminal has a front case and a rear case. A printed circuit board is accommodated into a cavity formed between the front case and the rear case and the rear case has a concave section on the surface of the outside of the rear case. The side wall of the rear case is formed to have the thick thickness and form a concave section. The concave section is portioned into a cell room and an antenna room by ribs extending from the side wall.